Familial adenomatous polyposis (FAP) is an autosomal dominant condition caused by a germline mutation in the APC gene.

Classical familial adenomatous polyposis (FAP) is defined by the presence of >100 colorectal adenomas (cumulative count), autosomal-dominant inheritance and young age of onset of polyposis (mean age approximately 15 years).

Atypical/attenuated familial adenomatous polyposis (AFAP) is defined by the presence of fewer than 100 colorectal adenomas (cumulative count) and autosomal-dominant inheritance, with later onset of adenomas and cancer compared with classical FAP.

This risk management guideline has been developed for individuals who have NOT been diagnosed with a relevant cancer/tumour. The care of affected individuals should be individualised based on their clinical situation, and the monitoring they need as part of their treatment and post-treatment follow up.

*This data is from classical FAP and does not take the impact of surveillance into account#Penetrance of colorectal adenoma is almost 100% by age 40 in the classical FAPrr^there is a higher risk of desmoid tumour following surgery or pregnancy, with female gender, and with family history of desmoid tumoursrr

A systematic review found that registration, surveillance and colectomy have a consistent and significant reduction in incidence and CRC related mortality.r

Expert opinion is that children at risk for classic FAP are screened every 1 to 2 years by flexible sigmoidoscopy or colonoscopy, beginning at 10 to 12 years of age.rr

Those initially screened at an older age should probably have colonoscopy for the first examination.r If surgery is delayed longer than a year after polyps emerge, annual colonoscopy should be used for surveillance.

In AFAP the emergence of adenomas and cancer is delayed 10 to 20 years compared with classical FAP. People with AFAP have fewer adenomas than those with classical FAP, although polyp number is variable within kindreds. As polyps have a more proximal colonic preponderance colonoscopy should be used for screening (not sigmoidoscopy), usually starting from late teens and repeated every 1 to 2 years depending on polyp burden.rr

The upper GI surveillance protocol is based on published literature and expert opinion.r

First degree (blood) relatives (parents/brothers/sisters/children) are at 50% risk of having inherited the gene mutation/or having the condition. First degree relatives should be referred to a local family cancer clinic.

Further References

The information contained in this document is based on the highest level of available evidence and consensus of the eviQ reference committee regarding their views of currently accepted approaches to care or treatment. Any clinician seeking to apply or consult this document is expected to use independent clinical judgement in the context of individual clinical circumstances to determine any patient's care or treatment. Use is subject to eviQ’s disclaimer available at www.eviQ.org.au